ignore node_modules for livereload

may allow perf boost

gulpfile.js

@@ -302,6 +302,7 @@ gulp.task('serve', () => {
     gulp.watch([
         slidesRoot + '**/*.html', 
         slidesRoot + '**/*.md',
+        `!${slidesRoot}**/node_modules/**`, // ignore node_modules
     ], gulp.series('reload'))
 
     gulp.watch(['js/**'], gulp.series('js', 'reload', 'eslint'))